Conventionally, core samples are obtained through the use of core drilling systems that comprise outer and inner tube assemblies. In operation, a cutting head is attached to the outer tube assembly so that rotational torque applied to the outer tube assembly can be transmitted to the cutting head. A core is generated during the drilling operation, with the core progressively extending along the elongate axis of the inner tube assembly as drilling progresses. Typically, when a core sample is acquired, the core within the inner tube assembly is fractured and the inner tube assembly and the fractured core sample contained therein are then retrieved from within the drill hole, typically by way of a retrieval cable lowered down the drill hole. Once the inner tube assembly has been brought to ground surface, the core sample can be removed and subjected to the desired analysis.
It is desirable for analysis purposes to have an indication of the orientation of the core sample relative to the ground from which it was extracted. This is complicated in that it is common to drill at an angle relative to the vertical. For efficiency and accuracy of the mineralogical record, it is desirable to determine the orientation and survey position of each core's position underground before being drilled out and extracted. Such orientation and survey positions allow for the subsequent production of a three dimensional map of underground mineral/rock content.
One common way of obtaining an indication of the orientation of a core sample is through use of an orientation spear comprising a marker (such as a crayon) projecting from one end of a thin steel shank, the other end of which is attached to a wire line. The orientation spear is lowered down the drill hole, prior to the inner tube assembly being introduced. The marker on the orientation spear strikes the facing surface of material from which the core is to be generated, leaving a mark thereon. Because of gravity, the mark is on the lower side of the drill hole. The inner tube assembly is then introduced into the outer tube assembly in the drill hole. As drilling proceeds, a core sample is generated within the inner tube assembly. The core sample so generated carries the mark which was previously applied. Upon completion of the core drilling run and retrieval of the core sample, the mark provides an indication of the orientation of the core sample at the time it was in the ground.
Other conventional technologies use core orientation units attached to core inner tubes and back-end assemblies to determine the correct orientation of the drilled out core sample after a preferred predetermined drilling distance intervals during drilling. These core orientation units typically measure rotational direction of the core sample before extraction. On retrieval at the surface of the hole, the rotational direction can be determined by electronic means and the upper or lower side of the core material physically ‘marked’ for later identification by geologists.
Coupled with the core orientation system, a survey instrument is conventionally used. In this technique, at periodic depths, the survey instrument is lowered down the drill hole to determine azimuth (angular measurement relative to a reference point or direction), dip (or inclination) and any other required survey parameters. These periodic depth survey readings are used to approximate the drill-path at different depths. Together with the rotational position of the extracted core (from the core orientation device), the three dimensional subsurface material content map can be determined.
It has been found desirable to provide an improved core barrel assembly having an integrated sample orientation subassembly and method for using same that is configured for use in a core sample down hole surveying and sample orientation that minimizes the need to add additional drill string elements, which allows for increased efficiency and speed of drilling.